1. Technical Field of the Invention
The present invention relates to integrated circuits, and more particularly to the formation of a metal silicide on an integrated circuit component.
2. Description of Related Art
The production of microelectronic components often includes a step of siliciding part of said component. The siliciding step consists in the formation of a metal silicide on a silicon zone. This step most particularly takes place on surfaces that are used as contact surfaces between the microelectronic component and the connection tracks. Silicidation makes it possible to achieve better conductivity at these surfaces thanks to the silicon/metal alloy thus formed, which has a very low contact resistance.
Silicidation methods are currently known and widely used.
Thus, a self-aligned silicidation method for an MOS transistor is conventionally used by those skilled in the art. According to this method, the metal to be silicided is deposited over the entire surface of the transistor, that is to say on the source, drain and gate regions, on the insulating spacers and on the isolating zone (for example of the shallow trench isolation type) which isolates the transistor from the other components of the integrated circuit. A heat treatment is then carried out during which the metal silicide forms between the silicon and the metal in the contact zones, that is to say in the source, drain and gate regions. However, there is no silicidation at the spacers and the isolating zone, which generally consist of silicon oxide or silicon nitride. Finally, the surplus metal remaining on top of the previously formed metal silicide and on top of the spacers and the isolating zone is removed using a chemical solution, the chemical solution being chosen so as to selectively remove the metal, and not its silicide.
Currently, CMOS technologies use nickel silicide (NiSi). An example of a chemical solution for selectively etching nickel and not its silicide is a mixture of sulphuric acid and hydrogen peroxide diluted in water, called an SPM (sulphuric peroxide mixture).
However, for future generations, it is intended to use other silicides, such as platinum silicide (PtSi) or iridium silicide (IrSi), which have a lower contact resistance and better stability. It is even envisaged to use silicides of rare earths (such as erbium (Er) or ytterbium (Yb)) for certain architectures.
In the case of platinum, the only currently known chemical solution capable of dissolving it is aqua regia, which is formed from a mixture of concentrated hydrochloric acid, concentrated nitric acid and water. However, aqua regia also attacks platinum silicide, and is therefore not selective with respect to platinum alone. In addition, aqua regia is a chemical solution that is highly corrosive and unstable over time. It is therefore a solution barely compatible with use in an industrial environment.
In the case of iridium, there is no known chemistry that allows it to be dissolved while leaving the silicide behind.
The chemical solution must therefore meet at least two constraints. Firstly, it must be capable of dissolving the unsilicided metal. Secondly, it must not dissolve the silicide of said metal, or do so only slightly. These constraints greatly limit the choice of chemical solution for the new metals envisaged and, in general, result in highly corrosive solutions that are therefore barely usable in an industrial environment.
There is a need to remedy these drawbacks.